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Flying Fish: Missiles of the Sea

Friday, June 25, 2010

Nature Notes
by Bob Thomas

Among the intriguing animals along the Louisiana coast are the flying fish. There are more than 50 species worldwide, with eight in the Gulf of Mexico, and they are most abundant in tropical and subtropical marine waters. Lucky for us, flying fish occur off the coast of Louisiana. It is a common creature of clear blue water, and schools of these fishes escape our attention when streaking through the water. When they decide to become airborne, the invisibility ceases and the spectacle begins.

Flying fish do not actually fly in the sense that a bird does by using its wings, instead, they glide* as discussed below.

Flying fish are perfectly designed for efficient use of both water and air. For water, they are long and thin, have a narrow caudal peduncle (narrow area just anterior to the caudal/tail fin), and the caudal fin is lunate (crescent-shaped). Fish with these characters, such as tuna, jacks, mackerel, and sailfish, are typically speed demons that pursue prey and avoid predation by being lissome and alacritous.

Characteristics that allow them to leave the water and glide through the air include enlarged pectoral fins that resemble wings and are set high on the sides of the body, enlarged pelvic fins that give them stability in the air, adaptations mentioned above that allow them to reach high speeds in the water, and the lower arc of the lunate caudal fin being elongated to resemble a rudder used in sculling.

When a flying fish decides it is time to go aerial, it accelerates to top speed by moving its caudal fin up to 70 times per second and, as the body leaves the water, it spreads its pectoral fins into an aerofoil (a wing that provides lift), the pelvic fins open, and it rapidly sways the enlarged lower lobe of its caudal fin in the water's surface to add speed to its exit.

Once aloft, they gain lift using oncoming winds or they take advantage of updrafts that come from the leading edges of waves, much like declivity currents along mountain ridges or bridges.

At the end of the flight, flying fish may simply fold their pectoral fins and drop into the sea, or they may drop the lower lobe of the caudal fin into the water, rapidly sway it back and forth, and launch back into the air to continue the flight.

First time viewers are often amazed at the sight of a fish flying through the air. They have been recorded gliding for 45 seconds* at speed over 40 miles per hour and covering over 1200 feet. They may reach over 20 feet above the sea. More than once, I have been in a boat moving over 30 mph and had to dodge a flying fish whizzing toward me, each time the fish luckily zipped past my head. A collision at that speed is not a story I want to be able to share.

Flying fish are considered neuston, specifically hyponeuston, meaning they are creatures inhabiting the ecosystem at the surface of the water. Hyponeustons live just below the surface, and epineustons (like water strider insects) work the top of the water. Living a hyponeuston lifestyle makes sense for a species that feeds mostly on plankton.

Though they are most frequently seen gliding away from the path of a boat, they can sometimes be seen rushing about beneath objects floating on the sea.

Flying fish lay eggs in the same hyponeuston zone that the adults occupy. An example is the Atlantic flying fish (Cypselurus melanurus) that lays its eggs among sargassum clumps. The eggs have many tiny strings on their surface that wrap around the parts of the sargassum, as well as one another. Clumps may become very dense, often sinking due to the added weight. If you find a very dense cluster of sargassum, check it closely. It may be a flying fish nest.

While we consider them a fascinating component of our marine ecosystem, they are a delicacy in Barbados (where they are the national fish) and Tobago.

A testament to their torpedo-shaped bodies and speed of movement, the Exocet missile got its name from flying fish, all of which are members of the Family Exocoetidae .
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* - from youtube.com